In semiconductor manufacturing, the inspection for defects on integrated circuit (IC) package and leads are common. Some of the defects require true three dimensional (3D) inspection. However, space constraints often limits the use of true 3D imaging that typically involves multiple cameras. Such constraints are particularly severe, in semiconductor packaging operation where an IC can only be viewed from a limited direction, such as the top. Thus space constraints precludes the use of multiple cameras viewing the IC from different directions. Fortunately, some of the defects can be determined by using implied 3D from 2D rather than true 3D imaging. Usually such defects are the type that do not need to be quantitatively determined. A qualitative approach is usually sufficient and hence true 3D imaging is not necessary.
Previous inspection systems employing 3D imaging techniques include the use of laser scanning to detect bent lead (downward or upward), pit, dent and other similar defects. A laser scanning method that involves the use of a laser to scan the surface of the object and detect the dispersion of the laser beam has also been used. Another approach of the laser scanning method is to detect the height (Z dimension) of the object through the use of laser triangulation. The three dimensional profile of the object surface can be determined and compared with a known good sample. Whilst these systems are effective, they suffer from the disadvantages of being expensive to implement and relatively slow due to the time required for the laser to scan the surface to complete the inspection.